1. Field of the Invention
The present invention relates generally to satellite communication systems, and more generally to hybrid-tee couplers utilized in satellite communication systems.
2. Related Art
In today's modern society satellite communication systems have become common place. There are now numerous types of communication satellites in various orbits around the Earth transmitting and receiving huge amounts of information. Telecommunication satellites are utilized for microwave radio relay and mobile applications, such as, for example, communications to ships, vehicles, airplanes, personal mobile terminals, Internet data communication, television, and radio broadcasting. As a further example, with regard to Internet data communications, there is also a growing demand for in-flight Wi-Fi® Internet connectivity on transcontinental and domestic flights. Unfortunately, because of these applications, there is an ever increasing need for the utilization of more communication satellites and the increase of bandwidth capacity of each of these communication satellites. Additionally, typical satellite beam service regions and applied levels are fixed on satellites and providers cannot generally make changes to them once a satellite is procured and placed in orbit.
Known approaches to increase bandwidth capacity utilize high level frequency re-use and/or spot beam technology which enables the frequency re-use across multiple narrowly focused spot beams. However, these approaches typically utilize input and output hybrid matrix networks which generally require very wide bandwidth hybrid elements within the hybrid matrix networks. This also usually includes a need for greater power amplification and handling within these hybrid matrix networks. Unfortunately, known hybrid elements generally result in variable and unconstrained phase splits across the ports of the hybrid matrix network that require special treatment in order to phase correctly within a matrix amplifier associated with the hybrid matrix network. Specifically, known hybrid elements such as hybrid couplers are typically limited bandwidth devices that do not operate well at very wide bandwidths.
Specifically in FIG. 1, a top perspective view of a known hybrid coupler 100 is shown. It is appreciated by those of ordinary skill in the art that the hybrid coupler 100 is generally referred to as a “magic-T” coupler (also known as a “Hybrid-T junction,” “Hybrid-Tee coupler,” or “Magic Tee coupler”). The hybrid coupler 100 includes a first waveguide 102 defining a first port 104, a second waveguide 106 defining a second port 108, a third waveguide 110 defining a third port 112, and a fourth waveguide 114 defining a fourth port 114. In general, the first waveguide 102 and second waveguide 106 are collinear and the first 102, second 106, third 110, and fourth 114 waveguides meet in a single common junction 118. The hybrid coupler 100 is a combination of an electric (“E”) and magnetic (“H”) “tees” where the third waveguide 110 forms an E-plane junction with both the first waveguide 102 and the second waveguide 106 and the fourth waveguide 114 forms an H-plane junction with both the first waveguide 102 and the second waveguide 106. It is appreciated that the first 102 and second 106 waveguides are called “side” or “collinear” arms of the hybrid coupler 100. The third port 112 is also known as the H-plane port, summation port (also shown as Σ-port), or parallel port and the fourth port 116 is also known as the E-plane port, difference port (also shown as A-port), or series port.
The hybrid coupler 100 is known as a “magic tee” because of the way in which power is divided among the various ports 104, 108, 112, and 116. If E-plane and H-plane ports 112 and 116, respectively, are simultaneously matched, then by symmetry, reciprocity, and conservation of energy the two collinear ports (104 and 108) are matched, and are “magically” isolated from each other.
In an example of operation, an input signal 120 into the first port 104 produces output signals 122 and 124 at the third 112 (i.e., E-plane port) and fourth 116 ports (i.e., H-plane port), respectively. Similarly, an input signal 126 into the second port 108 also produces output signals 122 and 124 at the third 112 and fourth 116 ports, respectively, (but unlike the output signal 124) where the polarity of the resulting output signal 122 corresponding to the input signal 126 at the second port 108 is of an opposite phase (i.e., 180 degrees out of phase) with respect to the polarity of the resulting output signal 124 corresponding to the input signal 120 at the first port 108. As such, if both the input signals 120 and 126 are feed into the first 104 and second 108 ports, respectively, the output signal 124 at the fourth port 116 is a combination (i.e., a summation) of the two individual output signals corresponding to each input signal 120 and 126 at the first 104 and second 108 ports and the output signal 122 at the third port 112 is a combined signal that is equal to the difference of the two individual output signals corresponding to each input signal 120 and 126 at the first 104 and second 108 ports.
An input signal 128 into the third port 112 produces output signals 130 and 132 at the first 104 and second 108 ports, respectively, where both output signals 130 and 132 are of opposite phase (i.e., 180 degrees out of phase from each other). Similarly, an input signal 134 into the fourth port 116 also produces output signals 130 and 132 at the first 104 and second 108 ports, respectively; however, the output signals 130 and 132 are in phase. The resulting full scattering matrix for an ideal magic tee (where all the individual reflection coefficients have be adjusted to zero) is then
  S  =                    1                  2                    ⁡              [                                            0                                      0                                      1                                      1                                                          0                                      0                                                      -                1                                                    1                                                          1                                                      -                1                                                    0                                      0                                                          1                                      1                                      0                                      0                                      ]              .  
Unfortunately, this hybrid coupler 100 is assumed to be an ideal magic tee that does not exist in the reality. To function correctly, the hybrid coupler 100 must incorporate some type of internal matching structure (not shown) such as a post (not shown) inside the H-plane tee (i.e., fourth port 116) and possibly an inductive iris (not shown) inside the E-plane (i.e., third port 112). Because of the need to some type of internal matching structure inside the hybrid coupler 100, which is inherently frequency dependent, the resulting hybrid coupler 100 with an internal matching structure will only operate properly over a limited frequency bandwidth (i.e., over a narrow bandwidth).
Therefore, there is a need for an improved hybrid matrix network and corresponding hybrid element that addresses these problems.